LARGE-SCALE AUGMENTATIVE BIOLOGICAL CONTROL OF ASIAN CORN BORER USING TRICHOGRAMMA IN CHINA: A SUCCESS STORY

Transcription

1 Large-Scale Augmentative Biological Control of Asian Corn Borer Using Trichogramma LARGE-SCALE AUGMENTATIVE BIOLOGICAL CONTROL OF ASIAN CORN BORER USING TRICHOGRAMMA IN CHINA: A SUCCESS STORY Zhenying WANG 1, Kanglai HE 1, and Su YAN 2 1 State Key Lab for the Biology of the Plant Diseases and Insect Pests Institute of Plant Protection, Chinese Academy of Agricultural Sciences Beijing , China 2 National Agro-technology Extension and Service Center Ministry of Agriculture Beijing , China ABSTRACT Asian corn borer, Ostrinia furnacalis (Guenée), is the most destructive pest of corn in China. It causes 6 to 9 million ton yield loss in an average year. Biological control using releases of Trichogramma has increased greatly since T. dendrolimi Matsumura can be successfully mass reared on eggs of the Chinese oak silkworm, Antheraea pernyi Guérin-Méneville. The process and technique for mass production and releasing of Trichogramma has been greatly improved in recent years. A series of machines and devices for mass rearing the Trichogramma with the eggs of oak silkworm has been developed, which promote Trichogramma production and make application for control of the Asian corn borer more practical and efficient. Asian corn borer control by release of T. dendrolimi on a large scale has been the key pest management technique in North China. In T. dendrolimi release areas parasitism of corn borer eggs ranged from 73.4% to 87.8%, with a 92.5% decrease of stalk-boring. Overall, augmentative releases have been made on 4.1 million ha of corn from 1990 to 2002 in Jilin Province with good pest control effects. T. dendrolimi and T. chilonis have been successfully produced by means of artificial host eggs and releases of these have had similar effects to the same species reared from factitious host eggs. Field application techniques also have been greatly improved. Large ecological and economic benefits have been achieved in the area where Trichogramma have been released continuously for many years. In Miyun County of Beijing, where Trichogramma have been released for more than 20 years, populations of natural enemies in cornfields have increased, which allow natural control of other insect pests without application of pesticides. Parasitism due to natural Trichogramma increased from 1% and 79.3% in 1980 to 33% and 92% in 1991 for first and third generation of Asian corn borer eggs, respectively. In Gongzhuling City, Jilin Province, the mean borer holes and number of larvae per hundred stalks decreased by 73.66% and 75.93%, respectively, where the Trichogramma were released from 1990 to In recent years Trichogramma releases for control of Asian corn borer cover 1 to 1.3 million ha annually, and have become one of the key techniques for IPM of corn pests in China. 487

2 Wang et al. 488 INTRODUCTION Corn (Zea mays L.) is playing a very important role in grain production in China. Among the grain crops grown in China, corn ranks second after rice in planting area, total yield and average yield. The average annual planting area is 24 million ha, total yield is 125 million ton, the average yield was 4,839 ton/ha. China is also the second largest corn production country in the world. The Asian corn borer, Ostrinia furnacalis (Guenée), is distributed in East and Southeast Asian countries, such as China, Japan, Korea, Thailand, The Philippines, Indonesia, Malaysia, and some islands in the Pacific Ocean (Nafus and Schreiner 1991). It causes serious damage to corn, sorghum, millet and cotton. It remains the most significant economic insect pest of corn in China. Estimated average annual losses in China due to this insect range from 6 to 9 million tons. These losses can be much greater in an outbreak year (Zhou and He 1995). In China, the Asian corn borer is distributed in most corn growing areas. It goes through one to seven generations a year from the far northern Heilongjiang Province to the southern Hainan Province, according to different latitudes and elevations (All China Corn Borer Research Group, 1988). Among these, one- to three-generation areas are of greater economic importance, owing to the extensive cultivation of corn in these regions. The generations that occur in whorl stage corn cause more serious direct reduction in yield than those that occur in the silking/pollen-shedding stages (Zhou and He 1995). However, the indirect yield loss caused by the generations occurring in later crop stages is much greater than that in whorl stage because the larvae feed on silk and kernels inducing ear and kernel rot which result in contamination of corn grains by mycotoxins produced by fungi, such as Aspergillus, Fusarium, and Penicillium. Since the early 1950s, a comprehensive study of utilization of the egg parasitoid Trichogramma has been conducted for controlling Asian corn borer. Shandong Academy of Agricultural Sciences successfully produced Trichogramma dendrolimi Matsumura on the Chinese oak silkworm, Antheraea pernyi Guérin-Méneville in the 1960s (Wang 2001). As the eggs of A. pernyi were used as host for mass rearing Trichogramma in 1970s, research and application of Trichogramma have expanded in China and it has been widely used in the successful biological control of many insect pests, especially the Asian corn borer in North China (Gou 1986). Since 1983, the Chinese government has funded National IPM Technique Research Projects as one of the State Key Research Programs in four successive State Five-year Plans. Biological Control Technique Research is one of those research projects. Since then, there have been improvements in process and technique for mass production and releasing of Trichogramma, especially for the Asian corn borer. TRICHOGRAMMA SPECIES USED FOR ASIAN CORN BORER IN CHINA There are 12 Trichogramma species identified from parasitized Asian corn borer eggs throughout China. Among them, T. dendrolimi, T. chilonis Ishii, T. ostriniae Pang et Chen, and T.

3 Large-Scale Augmentative Biological Control of Asian Corn Borer Using Trichogramma evanescens Westwood are distributed throughout the country, and T. leucaniae Pang et Chen, T. poliae Nagaraja, T. closterae Pang et Chen, T. pintoi Voegele, T. ivelae Pang et Chen, T. exiguum Pinto and Platner, T. forcipiformis Zhang and Wang, and T. tielingensis Zhang and Wang are distributed in some regions. T. ostriniae is the dominant species attacking the Asian corn borer in most corn growing regions of China, comprising from 72.2% to 100% of the Trichogramma. However, T. dendrolimi comprises 97.3%, 28.9% and 45.1% of the total Trichogramma in Heilongjiang, Jilin, and Liaoning Provinces in Northeast China, respectively, and T. chilonis comprises 88.9% of all Trichogramma in Guizhou Province in Southwest China. T. ostriniae accounts for up to 90% of the total parasitized Asian corn borer eggs in Beijing (Zhang et al. 1990). Although T. ostriniae is the dominant species attacking Asian corn borer eggs in China and it is more effective for corn borer control than T. dendrolimi, the cost for mass rearing T. ostriniae is higher and the production efficiency is lower. This species can only be mass reared on small eggs, such as the rice grain moth eggs, Corcyra cephalonica, and not use oak silkworm eggs or artificial host eggs. As a result the application of T. ostriniae is limited in practice (Feng 1996). T. dendrolimi and T. chilonis are the two Trichogramma species which can be mass reared on the eggs of A. pernyi and artificial host eggs. Some field releases showed that T. chilonis provided better control for Asian corn borer control in some areas than T. dendrolimi (Feng et al. 1999; Tan 1999; Wu et al. 2001). In northeastern China, the Chinese oak silkworm is reared on oak tree as sideline occupation in forest regions. The Chinese oak silkworm cocoons are harvested in autumn and transported to biological stations throughout the country, and then stored in cool room for Trichogramma mass rearing the following year. The cocoons of oak silkworm can be stored under -5 C for 5 months. In the early summer, the cocoons are hung in the emerging room before mass rearing begins. The eggs squeezed from abdomens of female moths are better for parasitization of Trichogramma. These eggs are obtained by squeezing female moth abdomens 1 or 2 days after adult emergence, where upon they are washed and dried. Each female moth can produce 200 eggs and between wasps emerge from each egg. A number of 60 per egg is optimal and more than 80% of emerged adult parasitoids are females (Liu et al. 2000). Procedures and equipment for mass production of T. ostriniae by using Sitotroga cereallela (Olivier) eggs have been developed and T. ostriniae will be available for improved Asian corn borer control in the near future (Jia et al. 2002; Zheng et al. 2003) 489 IMPROVEMENT OF MASS PRODUCTION OF TRICHOGRAMMA USING CHINESE OAK SILKWORM EGGS Given the large size of an oak silkworm egg, adjustments must be made in the ratio of female wasps to host eggs as well in the exposure time to avoid superparasitism and degeneration. For oak silkworm eggs, the optimum ratio between the number of parent female wasps and host eggs is 2:1. The optimum time of exposure is shorter than 24h. The parasitism of fresh eggs usually reaches 90% (Liu et al. 2000).

4 Wang et al. 490 At least 5 different production components have been developed, which are basically composed of (1) collection of Trichogramma from the field that are then cultured on host eggs and reserved as founder population for the following year; (2) selection of host eggs and their storage, and (3) mass propagation (Piao and Yan 1996). The selection of female cocoons which will produce host eggs and treatment of host eggs have been mechanized. A set of machines and devices has been designed, which includes machines for collecting emerged silkworm moths, squeezing of female moths, washing and drying host eggs, preparing egg cards, and parasitizing eggs (Liu et al. 1980; Liu et al. 1991; Song et al. 1994). Equipment for separating immature eggs from mature eggs was also developed. An automatic production line, with the capacity of producing 40 billion Trichogramma annually was established in Jilin (Song et al. 1994). The procedure for Trichogramma mass production has been simplified. Trichogramma spp. are reared simply by the method of releasing wasps in a small empty room with the egg cards on glass windows or on hanging screens (room-rearing). Sometimes the parasitized host eggs (before emergence of Trichogramma) are mixed with fresh unparasitized host eggs on wooden trays. When the wasps emerge, they parasitize the host egg directly. Every day in such biological stations million wasps are produced (Liu et al. 2000). To maintain high quality of Trichogramma reared on oak silkworm eggs, an instrument for selecting healthy parasitized host eggs was designed. It can distinguish parasitized from unparasitized host eggs, and healthy from infected host eggs based on the elasticity of parasitized host eggs (Wang et al. 1999). In addition, the processes of mass production, quality control and field release are standardized in Jilin, Liaoning and Beijing in North China (Piao and Yan 1996). Technical regulations for T. dendrolimi mass production using A. pernyi eggs were standardized in 2004 and await approval. This will regulate procedures for Trichogramma production and improve the quality of the parasitoid using A. pernyi eggs in China. TRICHOGRAMMA SUCCESSFULLY MASS REARED ON ARTIFICIAL HOST EGGS Research conducted since 1975 in China has resulted in successful rearing of Trichogramma in vitro on artificial host eggs. Breakthroughs have been made on the rearing of T. dendrolimi and T. chilonis by means of artificial eggs and further research has shown that their efficacies were similar to the same species reared from factitious eggs. Oviposition synergists that improved oviposition by T. dendrolimi and T. chilonis were selected (Han et al. 1994). With the addition of tricosane in a polyvinyl alcohol hydrophilic colloid, parasitism and pupation of T. dendrolimi on artificial host eggs reached 100% and 81.25%, respectively (Zhang 1993). The system closest to commercial production is that developed for T. dendrolimi on a basis of insect hymolymph. This diet has been packaged in plastic host egg-cards. Mechanized production of T. dendrolimi and T. chilonis with artificial host eggs has been successful. A model GD-5 automatic machine for mass production of artificial host egg cards was successfully created in 1995, and the technological process of Trichogramma produced with artificial host egg cards was developed. A computer controlled machine automatically completes all five

5 Large-Scale Augmentative Biological Control of Asian Corn Borer Using Trichogramma processes for egg production including setting-up the synthetic membrane, forming the egg shells, injecting the artificial media into the shells, sealing the double-layered membrane, and separating into egg cards. Operating rules for mechanized production of artificial host eggs for Trichogramma and techniques for propagating parasitoids, quality control, and releasing were formulated (Dai et al. 1996; Liu et al. 1996). Two artificial host egg production lines for Trichogramma were set up in Guangzhou and Beijing in the late 1990s. The parasitoids from in vitro rearing have been used on more than 150,000 ha with parasitism and control effects equal to parasitoids from natural host eggs (Wang 2001). Field experiments showed that the egg parasitism was 65.44% to 68.16%, when using T. dendrolimi and T. chilonis reared on artificial host eggs to control summer corn borer. In comparison with chemical control, the percentage of tunnels and broken tassels was reduced by 66.67% to 70.37%, and 73.33% to 80.00%, respectively. T. chilonis also showed good control of corn earworm, Helicoverpa armigera, on corn with 71.1% control, significantly better than that of T. dendrolimi (20% control) (Feng et al. 1999). China is the first country to make use of in vitro rearing of Trichogramma for commercial production and use on a large scale (Wang 2001). IMPROVEMENT OF FIELD APPLICATION TECHNIQUES FOR TRICHOGRAMMA AND CONTROL EFFICACY Field application techniques have been greatly improved since the 1980s. Release sites have decreased from 90 to 45 per ha based on the dispersal distance of T. dendrolimi in the field. The frequency of release has decreased from 3 to 2 and the number of Trichogramma released has increased from 135,000 wasps to 150, ,000 wasps/ha. Release timing is determined by monitoring of Asian corn borer pupation rate. When the pupation rate of the overwintering generation is 10%, the first release is made 10 days later. The second release is usually done seven days after the first release. Parasitoid releases have shown consistent levels of 60-85% parasitism, with reductions in damage of 65-92% (Piao and Yan 1996). Meanwhile, longperiod egg cards were exploited for corn borer control by mixing different stages of Trichogramma development on a card, thereby staggering emergence, so that only one or a few releases need to be made. This approach ensures that there are always some females actively searching throughout host oviposition (Zhang et al. 1993). The mean parasitism of Asian corn borer egg masses was 76% compared with 12% in the uncontrolled area on a 72,400 ha scale trial in 1988 in Yushu City, Jilin Province. The parasitism of corn borer eggs by T. dendrolimi ranged from 73.4% to 87.8%, with a 92.5% decrease of the stalk-bore rate (Liu et al. 2000). Overall, releases were made in 4.1 million ha of corn from 1990 to 2002 in Jilin Province with good control efficacy. In two-generation areas, additional Trichogramma release was needed when the egg masses of the second generation were observed, leading to an average reduction of % for the overwintering population of Asian corn borer. The strategy for controlling the Asian corn borer in twogeneration areas consists of inundative release for the first generation, and inoculative release for the second generation. This strategy has been exploited on a large-scale in Liaoning Province where it has resulted in sustainable management of Asian corn borer (Cong et al. 2000). Where large pest outbreaks occurred chemical insecticide granules and Bacillus thuringiensis were applied in the late whorl stage. 491

6 Wang et al. 492 Large ecological and economic benefits have been achieved in areas where Trichogramma have been released continuously for many years. In Miyun County of Beijing, where Trichogramma have been released for more than 20 years, the populations of natural enemies in corn fields have increased. This helps keep other insect pests under control without application of pesticides. Parasitism due to natural Trichogramma increased from 1% and 79.3% in 1980 to 33% and 92% in 1991 for first and third generation eggs of the Asian corn borer, respectively (Shi 1996). The number of overwintering larvae was reduced to 5.6 larvae per hundred stalks with a yield of 7500 kg/ha in Xifeng County, Liaoning Province, where Trichogramma was released continuously on a large scale for over 30 years, compared with larvae per hundred stalks and 5250 kg/ha in other surrounding counties when the Asian corn borer outbreak occurred in 1997 (Cao and Sun 2002). In Gongzhuling City, Jilin Province, mean bores and number of larvae per hundred stalks decreased by 73.66% and 75.93%, respectively, where the Trichogramma were released from 1990 to Trichogramma release for control of the Asian corn borer has become one of the key techniques of IPM of corn pests in China (Wang et al. 2003). It has been commonly adopted by the farmers in the northeastern provinces in China because of its easy use and good control efficacy. Trichogramma releases to control Asian corn borer comprise 1 to 1.3 million ha each year. With the Chinese government paying attention to grain production and environmental protection, the technique has been expanded to the Huang-Huai-Hai summer corn region and the Northwestern corn region in recent years. The Jilin, Liaoning and Heilongjiang provincial governments have provided some subsidies for controlling the Asian corn borer with Trichogramma in recent years. This has expanded the Trichogramma release area to 2 million ha in REFERENCES All China Corn Borer Research Group Studies on the identification of the dominant corn borer species in China. Acta Phytophylacica Sinica 15, Cao, J. L, and Sun, H. J Control effect analysis for Asian corn borer by releasing Trichogramma dendrolimi. Rain Fed Crops 22, 116. Cong, B., Yang, C. C., Yang, S. W., Li, Y. Q., Wen, H., Liu, W., Yi, Y. Q., Fu, B., and Chen, G Establishment, development and perspective of IPM of maize diseases and pest insects in Liaoning Province. Journal of Shenyang Agricultural University 31, Dai, K. J., Ma, Z. J., Pan, D. S., Xu, K. J., and Cao, A. H Standardization on Mechanized Production of Artificial Host Eggs of Trichogramma and Techniques for Propagating Wasps. In Proceedings of the National Symposium on IPM in China (Z. L. Zhang, Y. F. Piao, and J. W. Wu, Eds.), pp China Agricultural Scientech Press, Beijing. Feng, J The effect and influence factors on the use of Trichogramma dendrolimi to control Ostrinia furnacalis. Entomological Journal of East China 5,

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